Phenomenon

A phenomenon (plural phenomena) is an event that has been observed and considered factual, but whose cause or explanation is considered questionable, unknown, or not well researched.

As an example, "Many people claim to have seen the phenomena of UFOs and firmly believe what they've seen something genuine, but science continues to have doubts about their existence." In psychology, phenomena consist of frequently seen human behaviors such as the bystander effect in which as the number of witnesses to a mishap or accident increases the likelihood that someone will help decreases.